It is known to display a remaining charge time by using a map showing the relationship between the battery capacity accumulated in the battery and the battery terminal voltage to identify a battery capacity (SOC) that is charged at the current time from the terminal voltage, by storing a plurality of such maps corresponding to the plurality of charge currents, and by referring to the maps to acquire the remaining charge time corresponding to the SOC and the charge current (for example, see Japanese Patent Application Publication No. 2011-91879).
However, the battery terminal voltage may vary depending on a magnitude of a charge current, etc. Thus, it is difficult to calculate and display the remaining charge time accurately from a map showing the relationship between the SOC and the terminal voltage.